1. Field of the Invention
The present invention relates to a therapeutic agent for the treatment of mastitis in livestock, and a method for treating mastitis using the same. Particularly, the present invention relates to a therapeutic agent and method for the treatment of mastitis in livestock during lactation periods.
2. Description of the Related Art
Mammals described as livestock, for example, cattle, horses, goats, sheep, pigs and rabbits, all possess a mammary gland and therefore may develop mastitis. Livestock that are frequently milked, for example, cattle and in particular the milk cow, are most liable to develop mastitis. Mastitis is one of the most difficult diseases to cure for the milk cow. Mastitis tends occur more frequently in recent years due to milking stress as a result of large scale breeding of cows and wide spread use of milking machines. Consequently, the mammae of cows often develop mastitis, with an incidence of as high as ¼ of the total milk cows, including subclinical cows.
It has been reported that the number of somatic cells in cow's milk increases with the development of mastitis, and the disease adversely affects the quality and flavor of the dairy products. The number of the somatic cells (referred to as somatic cell counts, SCC hereinafter) in the raw milk of a healthy cow is 500,000 cells/mL or less. In contrast, SCC in the raw milk of a cow with mastitis reportedly increases to 1,600,000 cells/mL or more. According to statistical studies, the milk production of the cow decreases by 0.4 kg a day and 0.6 kg a day in primipara cow and multipara cow, respectively, for every increase of twice as much as SCC of 50,000 cells/mL or less. The fat content of the raw milk is also reported to decrease at a rate of 0.2 g/kg for every increase of twice as much as SCC (Am. J. Vet. Res., vol. 29, 497, 1968).
Naturally, distribution of the milk collected from cows infected with mastitis is suspended. Accordingly, economic losses caused by this disease are substantial.
Mastitis is a highly intractable disease, firstly because it is induced by a variety of microorganisms. Representative causative microorganisms include Staphylococcus aureus, Streptococcus agalaotiae, Streptococcus dysgalactias, Escherichia coli and Corynebacterium pyogenes. Infection by these microorganisms, is triggered by the stress such as large-scale breeding and wide spread use of the milking machines on the cow. Therefore, the number of infected cow Is increasing each year.
A second reason for the intractability of mastitis is that because it is considered along with other microbial diseases, and protection from mastitis relies too much on the use of highly potent antibiotics. Too much reliance on the antibiotics tends to neglect the importance of studies of pathological mechanisms of the onset of the disease and chronic infection mechanisms. It has been common means of treatment to select from and inject antibacterial agents such as furan and sulfur agents and antibiotics such as penicillin, sefem, streptomycin, tetracycline and macrolide based antibiotics.
However, these antibacterial substances may affect human health because the resistant bacteria occur due to residual antibacterial substances in the milk. Consequently, the period of use of these antibacterial substances is strictly restricted. Use of these antibacterial substances is also strictly restricted worldwide by a variety of regulations. Therefore, medication is often forced to be interrupted, even before sufficient remedial effects are achieved. As a result, dairy farmers are often troubled by recurrence of the disease and within a short time have to resume of medication.
A third reason for the intractability of mastitis is that the immune system of the mammary gland of milk cow differs according to the secretion and non-secretion periods of the milk secretion cycle (Vet. Immunol. & Immunopathol., vol. 65, 51-61, 1998; J. Diary Sci., vol. 82, 1459-1464, 1999). This may in fact be the main cause of the intractability of mastitis. That is, the modes of microbial infection in the mammary gland tissue are different, and infection protection mechanisms of the mammary gland itself may be very different during these periods.
During the active secretion period of as long as 10 months, the cells in the mammary gland and the immune system in the secreted milk is mainly composed of CD8′T-cells and γδ′T-cells that by themselves control epithelium cells concerning secretion of the milk. Accordingly, the immune function during this milk secretion period mainly operates by the cell-mediated immunity of Th1 (a group of helper T-cells).
The cells in the mammary gland and milk during the non-secretion dry period are mainly composed of leukocytes, CD4′T-cells and B cells originating from the blood and spinal cord. Accordingly, the immune function mainly operates by phagocytic response and humoral immunity mainly comprising antibodies and complements.
In other words, both periods involve quite contrasting immune mechanisms, and perform quite contrasting methods of protection against infection. Therefore, measures for protecting the animal from infection should naturally be different according to these periods. However, these features have not been taken into consideration in conventional countermeasures against infection.
Glycyrrhizin has been reported as having a variety of immunological functions in experimental animals such as mice. For example, glycyrrhizin stimulates the lymphocytes and induces production of IFN (interferon, Microbial. Immunol., vol. 26, 535-539, 1982) to enhance killer activities of the NK (natural killer) cells (Excerpta Medica International Conference Series, vol. 641, 460-464, 1983). In addition, glycyrrhizin is known to facilitate activation of the extra-thymus differentiated T-cells including γδ′T-cells and CD8′T-cells that are selectively distributed in the intestinal tract and mucosal organs independently of the thymus of the mouse (Biotherapy, vol. 5, 167-176, 1992). Otherwise, glycyrrhizin is known to facilitate a boost-up of cellular immunity based on the activation of the helper T-cells (in particular Th1 helper cells), thereby participating in protection of various virus infection diseases including retrovirus infection (Biotherapy, vol. 9, 209-220, 1996) and the suppression of allergic responses of the skin. Glycyrrhizin with protective effects against herpes virus induced death of the mucosal membrane (Immunol. Lett. vol. 44, 59-66, 1995) has also been proven to enhance immune activity with glycyrrhlzin in a mouse with immune deficiency that the skin is being burned.
The effect of glycyrrhlzin on microbial infection has been already tested on the human virus diseases, and the compound is reported to suppress viral hepatitis by oral and intravenous administration (Asian Med. J. vol. 26, 423-438, 1983; Microb. Immunol., vol. 44, 799-804, 2000).
In addition, glycyrrhizin has been used as an anti-inflammatory agent for external use on the human skin (Japanese Patent Laid-open No. 6-305932).
Further, glycyrrhizin has been used as a human nasal absorption drug as an absorption-accelerating agent (Drug Delivery System, vol. 4, 88-93, 1989).
However, although glycyrrhizin has been shown to have immunological functions in experimental animals such as a mouse and anti-inflammatory functions in humans, the idea for applying glycyrrhizin for mastitis of the livestock is unprecedented. Still more, the idea of applying glycyrrhizin to cow mastitis having complicated immune functions and caused by infection of various microorganisms is, too, unprecedented.